Ceramic burner for use in an air-preheater or hot blast stove for a blast furnace plant

ABSTRACT

A ceramic burner for the air preheater of a blast furnace plant is provided with a vertical core in at least the lower part of the fuel passage, which defines with the walls of the fuel passage a substantially slot-like and continuous passage around the core. The arrangement promotes uniformity of gas flow and uniformity of combustion over the entire surface of the slot-like burner head.

United States Patent [1 1 Lucieer et al.

[ 1 Sept. 24, 1974 Amerongen, Bennebroek, both of Netherlands [73] Assignee: Koninklijke Nederlandsche Hoogovens En Staal-Fabrieken N.V., Ijmuiden, Netherlands [22] Filed: Aug. 6, 1973 [21] Appl. No.: 385,666

Related US. Application Data [63] Continuation of Ser No. 141,855, May 10, 1971,

1,139,086 5/1915 Tidswell 239/553 1,533,909 4/1925 Ferguson 239/553 1,960,685 5/1934 Thompson et a1. 431/187 X 3,568,932 3/1971 Van Laar et a1 431/187 3,627,284 12/1971 Van Laar et a1 432/217 FOREIGN PATENTS OR APPLICATIONS 1,039,523 5/1953 France 239/4245 Primary Examiner-Carroll B. Dority, Jr. Attorney, Agent, or FirmHall & Houghton [5 7 ABSTRACT A ceramic burner for the air preheater of a blast furabandoned.

nace plant 18 provided with a vertical core in at least 2 H the lower part of the fuel passage, which defines with [5 1 U S Cl 7 432/217 431/187 34 5 25; the walls of the fuel passage a substantially slot-like 51 l Hm Cl F23l 9/04 and continuous passage around the core. The arrange- [58] Fie'ld /l 87 188 ment promotes uniformity of gas flow and uniformity 239/424 5 6 of combustion over the entire surface of the slot-like burner head.

[56] References Cited UNITED STATES PATENTS 4 4 Drawmg 485,594 11/1892 Adler 239/553 8 7 i I I 1 2 12 1o 12 9 y 6 6 I 4 13 ]I y Y CERAMIC BURNER FOR USE IN AN AIR-PREHEATER OR HOT BLAST STOVE FOR A BLAST FURNACE PLANT This is a continuation of application Ser. No. 141,855, filed May 10, 1971 abandoned.

This invention relates to a ceramic'bumer for use in an air preheater (hot blast stove) for a blast furnace plant, provided with a vertically extending air passage and a fuel passage within said air passage, said passages at their lower ends being connected to supply ducts for combustion air and fuel respectively. Moreover this invention relates to an air preheater provided with such a ceramic burner.

When manufacturing pig iron in blast furnaces the air for the blast furnace is preheated in so-called air preheaters or hot blast stoves. In modern embodiments of such stoves very often so-called ceramic burners are used of a type as indicated above, such burners being burners mainly existing of refractory brick material and built in the lower part of the burner stack of the air preheater. In such burners the air passage e.g. opens into a series of slot-shaped openings directed in an inclined manner towards the direction of discharge of a central slot-like opening of the passage for the gaseous fuel. This gives a very good mutual penetration of the gas and air flows which has for its purpose to give a uniform mixture of the correct mixing ratio for such components for the combustion.

Although this invention mainly relates to ceramic burners of which the openings of the gas and air passages are embodied in the given manner, the invention may also be applied with advantage to burners of different shapes such as burners of the type in which the gas and air passages are both split up into a considerable number of separate flows towards the exit openings, said flows alternating geometrically.

By a good shape and position of the openings of the gas and air passages it has appeared possible in principle to give an intimate mixing of gas and air.

However, special problems are encountered by the requirement that this mixture should also be uniform of composition over the entire surface of the head of the burner. If such a requirement is not fulfilled, there will be an incomplete combustion with a loss of efficiency as a result thereof, but also, even more important, the disadvantage that the air preheater cannot be heated up to the desired high temperature.

The uniformity of the composition of the mixture is dependent upon the velocity distribution of air and gas respectively within the passages near the openings thereof. This distribution of velocities should be constant also with time and should moreover be mutually corresponding for both passages. Thus the aim is to make both distributions of speed of gas and air as uniformly as possible.

In this respect it is remarked that the designer of the ceramic burner is considerably restricted in his design by the shape of the air preheater, the requirements to be made to the materials for use in the structure and moreover by the costs of the device.

The air passage does not give-the most serious problems in this respect as a result of the fact that this passage is formed as a slot-like passage extending around the gas passage. Such an annular slot appears to be a favourable shape for equalizing differences in air speed existing in the lower part of the air passage. At the discharge end of the burner the air flow is split up by a se' ries of slots, which again gives an equalizing effect on the distribution of this air flow.

The supply of the gas gives more difficulties in this respect. The gas passage is relatively short with respect to the dimensions in cross-section and moreover in practice an asymmetric supply of the gas to the gas passage is advantageous for design reasons in view of the mutual positioning and the ducting of the several stoves.

As a result thereof it is possible that at the discharge end of the burner differences in speed in the gas flow between several points of the discharge surface are measured amounting up to percent.

It is remarked that it has been suggested before to distribute the gas flow in a better way by applying pressure distributing and equalizing elements such as grids and the like in the gas passage. However, such parts, if operating adequately, cause a considerable loss in pressure and this is quite a disadvantage. In particular if low pressure gas such as blast furnace gas or coke oven gas is used, such grids or the like would require considerably high additional energies for the blowers etc.

According to the present invention a solution for the given problem was found which is simple from a viewpoint of design and which moreover is surprisinglyeffective. In this respect the invention consists in that at least in the lower part of the fuel passage a vertical core is present, which leaves between itself and the wall of the fuel passage a mainly continuous slot-like passage around the core as seen in cross-section.

The said core may consist of brick masonry built upon the bottom of the burner. It is also possible to make this core from a steel structure or to embody it in concrete.

Both for burners with circular as for burners with oval gas passages as seen in cross-section the novel structure gives an improvement of the gas distribution, without entraining a considerable loss of pressure over the length of the gas passage. The most surprising results were, however, obtained by applying the invention to a gas passage which in cross-section has a rectangular shape and in which the slot left around the core has a subtantially constant width all around. The improvement obtained in this way increases with a greater deviation of the passage from a pure square. However, also with a gas passage with an oval cross-section it is possible to obtain good results with a core which also has an oval cross-section. It will be clear that a very short core will not have much effect on the gasflow. On the other end it has appeared not to be favourable to have the core extend very closely to the discharge opening of the gas passage. In that zone the core would cause a disturbance of the flow pattern of the gas in said discharge opening.

It has appeared that optimum results may be obtained if according to the invention the core extends over somewhat more than the lower half of the fuel passage.

The danger of a disturbance of the flow pattern in the discharge opening by the presence of the core upstream thereof may be avoided by also having the upper end of the core tapering to a smaller crosssection. This-measure has as an additional advantage a decreased resistance to flow, which gives a saving in energy for the gas blowing means. 1

Finally this invention also relates to the air preheaters provided with such a ceramic burner according to the invention. It has appeared that such air preheaters can obtain a higher thermal efficiency by applying the invention therewith.

The invention will now be explained in more detail with reference to several diagrammatic drawings giving how the invention may be applied in a preferred embodiment.

FIG. 1 shows a ceramic burner and adjacent parts of a hot blast stove for a blast furnace plant in vertical section.

FIG. 2 is an enlarged, fragmentary, horizontal crosssection view taken on lines II-II of FIG. I to illustrate the positioning of the core to interrupt the gas passage in accordance with the present invention.

FIG. 3 gives speed curves for the gas.

FIG. 4 shows diagrammatically a hot stove on a much smaller scale, showing the position of the ceramic burner of FIG. 1 therein.

In FIGS. I and 4 reference numeral 1 shows part of the outer wall of a hot blast stove. Within said stove a wall 2 separates the burner stack from the pile of heat absorbing bricks known as such and not shown here in detail. Between wall part 1 and wall 2 a ceramic burner is provided in the burner stack in the lower part thereof.

With particular reference to FIG. 1, supply ducts 3 and 4 are intended to supply gas and air respectively and they are therefor connected to the gas passage 5 and the air passage 6. Passage 5 opens into the burner stack in the form of a rectangular opening. Passage 6 is divided at its upper end by diaphragms or intermediary walls 12 and thus opens in the shape of two rows of slot-like openings 8 not shown as such into the burner stack. The shape of the top face of the burner has been chosen in such a way that the air jets intimately penetrate the gas flow.

Restrictions 9 and 10 in passage 5 and 6 serve for the improvement of the uniform distribution of quantities in gas and air flows.

At the bottom of the burner stack a core Ill is built up, which extends up to some distance downwardly of the restriction 10. This masonry core is tapered at its upper end.

In FIG. 2 is an enlarged horizontal cross-sectional view illustrating the positioning of the core 11 in the gas passage 5. It appears therefrom that core 11 extends over substantially the whole length of gas passage 5. As will be seen, the space between the walls of the passage and the core has a substantially constant width on both longitudinal sides of the core.

EXAMPLE Through a ceramic burner of the type as shown diagrammatically in the drawings 120.000 Nm lh of gas and 180.000 Nm /h of air were passed by suitable blowers. The supply ducts 3 and 4 had diameters of about 180 cm.

The gas passage 5 has a height of 9 m and in crosssection, downwardly of restriction I0 has dimensions of 5 m and 0.75 m. Gas passage 3 is connected to the stove at an angle of 30 as will be clear from FIG. 2.

In FIG. 3 the abscissa shows length L of the discharge opening for the gas perpendicular to FIG. 1 and thus in the horizontal direction in FIG. 2. The ordinate gives gas speeds V in meters per second. Line a gives the distribution of the speed V which is measured in the gas flow over the length of the discharge opening 7, without core 11 being present in gas passage 5. In this graph it will be clear that the inciined blowing-in through supply duct 3 has the effect of a considerable asymmetry in the speed profile. Moreover, this speed differs between about l0 and I8 m/sec. Such considerable differences give rise to an unequal mixing of gas and air above the burner head and as a result thereof to a quite incomplete combustion.

After building up the core I l the same measurements were repeated. Core 11 has such a cross-section that it leaves a slot which along the long sides had a width of 30 cm and along the short sides had a width of IS cm. The height of the core was 300 cm.

Line b in FIG. 3 gives the result of these new measurements. It will be clear that the differences in speed have been reduced to less than 2 m/sec. It has appeared that no unburned gas parts remained above the burner head, as was checked by careful detections.

In a modified embodiment of core 11 this was, along the upper 50 cm of its length, extended to the left and right as seen in FIG. 2 to be in contact with the short walls of the gas passage 5. This gave the advantage that the core formed a more rigid and stable structure with the gas passage, so that it is also avoided that the core will vibrate by the gas flow. This appeared not to have a more than negligible effect on the distribution of the gas flow. In FIG. 1 these extensions are given as the dotted line at 13 and, although these extensions cannot be seen in the section of FIG. 2, as this was taken at a lower level, they have also been indicated in FIG. 2 by dotted lines 13.

What we claim is:

I. In a ceramic burner for use in a hot blast stove for a blast furnace plant wherein said ceramic burner includes a. means defining a vertically extending air passage therein, said passage having air openings,

b. means defining a fuel gas passage having in crosssection a substantially elongated rectangular shape and extending vertically within said air passage,

c. means for discharge of air at the exit end of said air passage, and

d. means defining horizontai air and fuel gas ducts communicating with said air and fuel gas passages respectively in a direction transverse to the axes of said passages and transverse to the longitudinal dimension of said rectangular shape,

the improvement comprising means to insure an intimate mixture of gas and air and of a uniform composition thereof over the entire burner surface, said means including e. a vertical core positioned at one end in the bottom of the fuel gas passage and f. said core extending generally centrally upwardly within said gas passage for a height greater than the diameter of the fuel gas duct and extending transversely across the path of the fuel gas entering horizontally from said fuel gas duct into the gas passage,

g. said core forming with the walls of the rectangular fuel passage a vertically extending slot-like and continuous rectangular fuel passage around the core,

5 6 h. said slot-like rectangular passage having a substan- 1, wherein tially Constan i th n e longitudinal Sides k. said core extends vertically upwardly in said fuel thereof,

i a rectangular discharge openings for said fuel at the upper end of said fuel passage, and

j. two rows of slot-like openings at the upper end of the vertically extending air passage on opposite passage to a height substantially greater than the height at which said fuel duct discharges transversely against said core.

3. An improved ceramic burner as claimed in claim sides of the rectangular discharge opening of said wherem fuel passage and angled toward the longitudinal core tapered at Its upper plane of said fuel passage so as to discharge air to- 4. A hot blast stove for a blast furnace comprising an ward the plane of said fuel passage. improved ceramic burner as claimed in claim 1. 2. An improved ceramic burner as claimed in claim 

1. In a ceramic burner for use in a hot blast stove for a blast furnace plant wherein said ceramic burner includes a. means defining a vertically extending air passage therein, said passage having air openings, b. means defining a fuel gas passage having in cross-section a substantially elongated rectangular shape and extending vertically within said air passage, c. means for discharge of air at the exit end of said air passage, and d. means defining horizontal air and fuel gas ducts communicating with said air and fuel gas passages respectively in a direction transverse to the axes of said passages and transverse to the longitudinal dimension of said rectangular shape, the improvement comprising means to insure an intimate mixture of gas and air and of a uniform composition thereof over the entire burner surface, said means including e. a vertical core positioned at one end in the bottom of the fuel gas passage and f. said core extending generally centrally upwardly within said gas passage for a height greater than the diameter of the fuel gas duct and extending transversely across the path of the fuel gas entering horizontally from said fuel gas duct into the gas passage, g. said core forming with the walls of the rectangular fuel passage a vertically extending slot-like and continuous rectangular fuel passage around the core, h. said slot-like rectangular passage having a substantially constant width on the longitudinal sides thereof, i. a rectangular discharge openings for said fuel at the upper end of said fuel passage, and j. two rows of slot-like openings at the upper end of the vertically extending air passage on opposite sides of the rectangular discharge opening of said fuel passage and angled toward the longitudinal plane of said fuel passage so as to discharge air toward the plane of said fuel passage.
 2. An improved ceramic burner as claimed in claim 1, wherein k. said core extends vertically upwardly in said fuel passage to a height substantially greater than the height at which said fuel duct discharges transversely against said core.
 3. An improved ceramic burner as claimed in claim 1, wherein k. said core is tapered at its upper end.
 4. A hot blast stove for a blast furnace comprising an improved ceramic burner as claimed in claim
 1. 